The grade 11, chapter 8 summary presentation on quantitative aspects of chemical change

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8. Quantitative aspects of chemical change
Chemistry
Grade 11

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Reactions and gases
●The volume of one mole of gas at STP is 22,4 dm3
● For any number of moles of gas at STP we can use to find the volume.
●The volume relationship for two gases in a reaction is given by:
where VA
is the volume of gas A, VB
is the gas B, a is the stoichiometric coefficient of gas A
and b is the stoichiometric coefficient of gas B.
Vg=22,4 ng
V A=
a
b
VB

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Solutions
The concentration of a solution can be calculated using:
where C is the concentration (in mol·dm3
), n is the number of moles of solute dissolved in the
solution and V is the volume of the solution (in dm3
).
A standard solution is a solution in which the concentration is known to a high degree of
precision. For the purposes of calculations, a standard solution can be thought of as one in
which the concentration is a set value.
A titration is a technique for determining the concentration of an unknown solution. We can
calculate the unknown concentration using:
where CA
and CB
are the concentrations of A and B (in mol·dm3
), VA
and VB
are the volumes of
A and B and a and b are the stoichiometric coefficients of A and B.
C=
n
V
CA V A
a
=
CB VB
b

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Stoichiometry
The following diagram is useful for stoichiometric calculations

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Stoichiometry calculations
1. Limiting reagents
A limiting reagent is a reagent that is completely used up in a chemical reaction.
An excess reagent is a reagent that is not completely used up in a chemical reaction.
This is determined by calculating the amount of product obtained from each reactant and then
seeing which reactant produces the least amount of product.
2. Percent yield
Percent yield is calculated using:
where the actual yield is the amount of product that is produced when you carry out the
reaction and the theoretical yield is the amount of product that you calculate for the reaction
using stoichiometric methods.
yield=
actual yield
theoretical yield
×100

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Stoichiometry calculations contd...
3. Empirical and molecular formulae
The empirical formula is the simplest formula of a compound.
The molecular formula is the full formula of a compound.
4. Percent purity
Percent purity is calculated using:
purity=
mass of compound
mass of sample
×100

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